1. Field of the Invention
The field of art to which the claimed invention pertains is hydrocarbon separation. More specifically, the invention relates to a process for separating a para-isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, the isomers having from 8 to about 18 carbon atoms per molecule which process employs a particular zeolitic adsorbent which selectively removes the para-isomer from the feed.
2. Description of the Prior Art
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate one hydrocarbon type from another hydrocarbon type. The separation of normal paraffins from branched chained paraffins for example can be accomplished by using a type A zeolite which has pore openings from 3 to about 5 Angstroms. Such a separation process is disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules. U.S. Pat. Nos. 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons from non-olefinic hydrocarbons.
In addition to being used in processes for separating hydrocarbon types, adsorbents comprising type X or Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the processes described in U.S. Pat. Nos. 3,558,730, 3,558,732; 3,626,020 and 3,686,342 for example particular zeolitic adsorbents are used to separate desired xylene isomers; in U.S. Pat. No. 3,114,782 they are used to separate alkyl-trisubstituted benzenes; in U.S. Pat. Nos. 3,864,416 they are used to separate tetraalkyl substituted aromatic hydrocarbon isomers and in U.S. Pat. No. 3,668,267 they are used to separate particular alkyl substituted naphthalenes.
The present process relates to a process for the separation of the para-isomer from a hydrocarbon feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the paraisomer, the isomers having from 8 to about 18 carbon atoms per molecule. We have found adsorbents comprising type Y zeolites essentially completely exchanged with a single cation selected from the group consisting of potassium, cesium, and rubidium exhibit selectivity for the para-isomer and possess other desired characteristics thereby making separation of the para-isomer by solid-bed selective adsorption processes possible.
The process is particularly useful in separating para-diethylbenzene and para-cymene from feed mixtures containing diethylbenzene isomers and cymene isomers respectively.